1. Field of the Invention
The present invention relates to a control valve of a type of electromagnetically proportional operation (an electromagnetic solenoid) used for an electronic-controlled power steering system (EPS) for a car. More particularly, it relates to an improvement in a coil bobbin installed in the control valve.
2. Discussion of the Background
There has so far been known a device as shown in FIG. 1 which was published, for example, in Japanese Utility Model Publication No. 35009/1982.
In FIG. 1, a reference numeral 1 designates a solenoid device, a numeral 2 designates a solenoid coil, a numeral 3 designates a plunger (movable iron core) capable of sliding in the direction of the arrow mark, a numeral 4 designates a push rod fixed to the top end of the movable iron core 3, a numeral 5 designates a valve body (an oil pressure valve body) connected to the front end of the solenoid device 1, a numeral 6 designates a spool which is arranged in the valve body 5 and is moved in its axial direction of the valve body 5 by pressure caused by the sliding movement of the plunger 3, a numeral 7 designates a spring bearing, a numeral 8 designates a spring and characters T, A and P designate oil pressure flow paths.
The operation of the solenoid device having the construction as described above will be illustrated.
When the solenoid coil 2 is actuated by current conduction from an external d.c. power source device, the movable iron core 3 is moved in the direction of the arrow mark to push the push rod 4. A pressing force of the push rod 4 is transmitted to the spool 6 and the spool 6 is caused to slide on the left hand in FIG. 1, pressing the spring 8. During the sliding movement of the spool 6, the oil pressure flow paths T, A and P are changed.
In the conventional device constructed as above-mentioned, since pressure oil (working oil) is filled in a space receiving the plunger 3, the pressure oil is apt to leak out to enter into the solenoid coil 2. Further, the inner diameter part of the solenoid coil 2 shrinks due to tension produced at the time of winding a coil thereby to cause difficulty in sliding movement of the plunger.